(1) Field of the Invention
The present invention relates to a novel process for recovering cyclodextrins.
Cyclodextrins are hydrolyzates obtained by reacting some gelatinized or liquefied starches with cyclodextrin glycosyltransferase. They are generally obtained by using cyclodextrin glycosyltransferase which is produced by microorganisms such as Bacillus macerans, Bacillus circulans and the like, or alkalophilic bacteria discovered by the inventors (See "Enzyme Handbook" edited by Shiro Akabori, published by Asakura Shoten (1966); Japanese Pat. No. 886,583, Japanese Patent Publication No. 31223/1978, U.S. Pat. No. 3,923,598, British Pat. No. 1,459,654 and French Pat. No. 74.37001). Cyclodextrins are non-reducing dextrins which have a crownlike structure wherein 6 to 12 glucose units are cyclically combined with one another by .alpha.-1,4-glucosidic linkage. It has recently been reported that some of such cyclodextrins have some branched structures wherein glucose units are combined by .alpha.-1,6-glucosidic linkage to form branched cyclodextrins. However, .alpha.-cyclodextrin, .beta.-cyclodextrin and .gamma.-cyclodextrin which consist of 6, 7 and 8 glucose units, respectively, are useful for industrial purpose. The cyclodextrin molecule has a doughnut-like shape and the interior of the hollow space formed by the molecule is in a hydrophobic atmosphere. On the other hand, the exterior and the opening of the hollow space are in a hydrophilic atmosphere. Such a specific structure of the cyclodextrin molecule is intimately concerned with the inclusion phenomenon thereof. The hollow space sizes of .alpha.-, .beta.-, and .gamma.-cyclodextrin molecules are known to be about 6 A, 8 A and 10 A respectively. As mentioned above, the cyclodextrin molecule includes some specific molecules the sizes of which conform to the hollow space size of the cyclodextrin molecule. Accordingly, cyclodextrins are widely usable in foods, medicines, cosmetics, agricultural chemicals and the like, and new applications thereof are expected.
(2) Description of the Prior Art
As described above, various processes for preparing cyclodextrins have been proposed. In conventional processes for preparing cyclodextrins, some gelatinized or liquefied starches are reacted with cyclodextrin glycosyltransferase, an organic solvent is added to the resulting starch hydrolyzates containing cyclodextrins to precipitate cyclodextrins, and the objective cyclodextrins in the hydrolyzates are separated from acyclic dextrins mixture. However, according to this process, the use of harmful organic solvents such as trichloroethylene, tetrachloroethane, bromobenzene, toluene or the like is inevitable, so that this process is undesirable in view of environmental sanitation laws which have become stricter in recent years. In addition, it is also disadvantageous from both the economical and industrial points of view.
In aother proposed process, the above-mentioned starch hydrolyzates containing cyclodextrins are reacted with a saccharified enzyme such as glucoamylase which hardly hydrolyzes cyclodextrins, thereby to hydrolyze acylic mixtures contained in the hydrolyzates to convert them into glucose, after which organic solvents such as ethanol, acetone or the like are added to the mixed sugar solution to selectively precipitate cyclodextrins, the cyclodextrins thus precipitated being separated thereafter (see "Starch Science" (DENPUNKAGAKU) Vol. 22, No. 1, pp. 6-10 (1975)).
In order to separate cyclodextrins effectively, it is desirable that the enzyme acts on the starch under a condition where the concentration is high. However, under such a condition, it has been found that obtaining a homogeneous gelatinization of starch is difficult and that the working thereof is very difficult due to its high viscosity. On the other hand, the use of low concentration starch also has many disadvantages because complicated means or expensive reagents are necessary to precipitate and separate cyclodextrins and at the same time, considerable costs are incurred to concentrate a sugar solution. Thus, in order to overcome these disadvantages a process for producing and separating cyclodextrins has been proposed, which is characterized in that cyclodextrin glycosyltransferase is reacted with a liquefied starch solution of a high concentration obtained by liquefying starch according to a conventional process, for example, by causing a small amount of .alpha.-amylase or acid to act on a starting starch solution (see Japanese Patent Publication No. 2380/1971).
However, organic solvents are used to precipitate produced cyclodextrins in all processes as described above, and the cyclodextrins thus obtained can not be utilized for medicines, foods and the like due to the toxicity of the solvents, which is the fundamental disadvantage in those processes.